This invention is in the field of cracking of hydrocarbons. Specifically this invention is in the field of reducing undesired polymerization of carbonyl compounds in unit operations of hydrocarbon cracking processes.
Pyrolysis is the transformation of a compound into one or more other substances by heat alone. In the petroleum and petrochemical industries, pyrolysis is useful for the processing of hydrocarbons. This process is often referred to as xe2x80x9ccrackingxe2x80x9d. When the pyrolysis of hydrocarbons is conducted in the presence of steam, it is often referred to as xe2x80x9csteam crackingxe2x80x9d. The steam cracking of ethane, propane, naphthas, gas oils and other hydrocarbon feedstocks is a useful process for producing valuable olefins. As a byproduct of the steam cracking process, oxygenated compounds, including carbonyl compounds, are formed. These carbonyl compounds include, but are not limited to, aldehydes and ketones. The amount of carbonyl compounds formed in cracking operations can vary widely, but is typically from about 1 ppm to about 200 ppm in the gas stream with concentrations as high as about 1000 ppm occasionally being encountered because of the use of various feedstocks and cracking temperatures.
Byproducts of hydrocarbon cracking processes include the undesirable acid gases CO2 and H2S. Therefore, it is normal for a hydrocarbon cracking plant to have an acid gas removal system to remove CO2 and H2S from the cracked gas. Typically the acid gas removal system usually consists of passing the gas steam through a basic wash (pH greater than 7) to remove acidic components, including hydrogen sulfide and carbon dioxide gas. In the petroleum and petrochemical industries, unit operations involving basic washes are commonly carried out in equipment referred to as xe2x80x98caustic scrubbersxe2x80x99 or xe2x80x98caustic towersxe2x80x99. As an alternative to a caustic tower, about 5% of all ethylene cracking plants use amine, instead of caustic, to remove acid gases. These units are often referred to as xe2x80x9camine scrubbersxe2x80x9d or xe2x80x9camine towersxe2x80x9d.
In an acid gas removal system, some oxygenated compounds are also removed. It is known in the art of hydrocarbon processing that certain of these oxygenated compounds, especially carbonyl compounds and particularly acetaldehyde, will undergo polymerization in the presence of the base. In the acid gas removal system, the acetaldehyde polymer will settle on internal equipment surfaces leading to fouling and eventual plugging. Fouling and plugging of the internal equipment means the unit must be shut down to perform cleaning. Every time a unit operation has to be shut down for cleaning it means that a cost is incurred due to lost production, over and above, the actual cost to clean the equipment.
In addition to the caustic scrubbers and caustic towers where treatment is required to inhibit fouling caused by unwanted polymerization, there are other basic wash unit operations in hydrocarbon processing that also require treatment in order to prevent undesirable polymerization of carbonyl compounds. These other basic wash unit operations include, but are not limited to, amine systems to scrub acid gasses (using higher-boiling aminoalcohols such as, but not limited to, ethanolamine, diethanolamine and derivatives of amino alcohols such as, but not limited to methoxyethylamine), spent caustic oxidizers and benzene strippers. A spent caustic oxidizer converts sulfides into sulfates to allow caustic to be disposed of, or to be sold. A benzene stripper is a unit that uses hydrocarbon, often a high boiling mixture called xe2x80x9cpyrolysis gasolinexe2x80x9d, taken from other units in the ethylene plant, to wash xe2x80x9cspent causticxe2x80x9d. xe2x80x9cSpent causticxe2x80x9d is caustic that has been used in other unit operations, such as the caustic tower. The hydrocarbon xe2x80x9cwashesxe2x80x9d residual benzene out of the spent caustic. The unit is called a benzene stripper because the benzene is stripped from the spent caustic.
Ten years ago the amount of undesired polymer that was formed in this way was usually insignificant. As hydrocarbon plants expanded their capacity, the amount of undesired polymer increased and the sheer volume of undesired polymer formed has now become a problem for more and more hydrocarbon plant operators.
Several materials are known and currently being used in the petroleum and petrochemical industries to mitigate carbonyl compound polymer caused fouling. These materials include dispersants, inhibitors, reducing agents and antioxidants.
U.S. Pat. No. 5,714,055 to Lewis et al. describes a method of inhibiting the formation of fouling deposits occurring on the surfaces of an alkaline scrubber used to wash acid gases generated during the manufacturing of olefins by using substituted aromatic amines selected from the group consisting of 2-aminophenol, 4-aminophenol, 4-aminobenzenesulfonic acid and salts thereof, 4-amino-o-cresol, 3-aminophenol, 2-aminobenzoic acid and salts thereof, 3-aminobenzoic acid and salts thereof, and 4-aminobenzoic acid and salts thereof.
U.S. Pat. No. 5,264,114 to Dunbar, describes and claims a method for inhibiting the formation and deposition of fouling materials during caustic washing of hydrocarbon gases contaminated with carbonyl compounds (one group of carbonyl compounds being aldehydes) which comprises: treating said hydrocarbon gases with an aqueous amine solution, wherein said aqueous amine solution comprises water and an amine compound having a concentration range of from about 2 ppm to about 5,000 ppm, and wherein the amine of said aqueous amine solution is selected from the group of organic compounds consisting of the formula RNH2 and R2NH wherein R is selected from the group consisting of alkyl groups and aryl groups, before said caustic washing, to remove a significant amount of said carbonyl compounds and to thereby produce a treated hydrocarbon stream.
U.S. Pat. No. 5,194,143 to Roling describes and claims a method for inhibiting the formation of polymeric based fouling deposits during the basic washings of olefin-containing hydrocarbons contaminated with oxygenated compounds comprising adding to the wash about 1 to about 10,000 parts per million acetoacetate ester compound having the formula
CH3COCH2CO2CxHy
wherein x is an integer from about 1 to about 8 and y is an integer from about 3 to about 17.
U.S. Pat. No. 4,952,301 to Awbrey describes and claims a method for inhibiting the formation of polymeric based fouling deposits which, in the absence of inhibition treatment, are formed during the basic washing of hydrocarbons contaminated with oxygen-containing compounds, said method comprising adding to the wash an inhibiting amount of an ethylenediamine compound of the formula
NH2(CH2CH2NH)xH
wherein x is an integer of from about 1 to about 10.
U.S. Pat. No. 4,673,489 to Roling describes and claims a method for inhibiting the formation and deposition of fouling materials during the basic washing of hydrocarbons contaminated with oxygenated compounds which comprises performing the wash of the hydrocarbon in the presence of a sufficient amount of hydroxylamine, of the formula NH2OH or an acid salt or mixtures thereof, for inhibiting the formation and deposition of foulant.
U.S. Pat. No. 5,220,104 to McDaniel et al. describes and claims a method for inhibiting the formation and deposition of fouling materials during basic washing of hydrocarbons contaminated with oxygenated compounds which comprises performing the washing of the hydrocarbons in the presence of a solution comprising a percarbonate compound in an amount sufficient to inhibit the formation and deposition of fouling materials.
U.S. Pat. No. 5,160,425 to Lewis describes and claims a method of inhibiting formation of polymeric fouling deposits during the caustic scrubbing of pyrolytically produced hydrocarbons contaminated with oxygen containing compounds with a basic washing solution having a pH greater than 7 comprising adding to the basic washing solution a sufficient amount of carbohydrazide for inhibiting formation of polymeric fouling materials.
U.S. Pat. No. 5,288,394 to Lewis et al. describes and claims a method of inhibiting formation of polymeric fouling deposits after the caustic scrubbing of a hydrocarbon stream contaminated with oxygenated compounds with a basic washing solution having a pH greater than 7 comprising adding to said hydrocarbon stream a sufficient amount for inhibiting formation and deposition of fouling materials of a composition comprising at least one hydrazide compound.
U.S. Pat. No. 5,770,041 to Lewis et al. describes and claims a method of inhibiting the formation of fouling deposits occurring in an alkaline scrubber used to remove acid gases, which deposits are formed during the scrubbing of pyrolytically produced hydrocarbons contaminated with oxygen-containing compounds with a caustic solution having pH greater than 7 which comprises adding an effective deposition-inhibiting amount of a non-enolizable carbonyl compound to the caustic solution.
U.S. Pat. No. 5,879,534 to Lewis et al., describes and claims a method of inhibiting the formation of fouling deposits occurring in spent caustic wash systems used for ethylene dichloride manufacturing processes which are in contact with ethylene dichloride processing streams contaminated with oxygen-containing compounds, which deposits are formed in ethylene dichloride processing streams contaminated with oxygen-containing compounds while in contact with a caustic solution having a pH greater than 7, which comprises adding an effective deposit-inhibiting amount of a non-enolizable carbonyl compound to said caustic solution.
It is desirable to identify additional compounds to inhibit this undesirable polymerization of carbonyl compounds in hydrocarbon cracking processes.
The first aspect of the instant claimed invention is a method to inhibit the polymerization of a carbonyl compound in a basic wash unit operation in a hydrocarbon cracking process, comprising:
contacting a stream comprising at least one carbonyl compound with a compound selected from the group consisting of
alpha-amino acids and esters thereof and amides thereof and salts thereof and mixtures thereof;
wherein said compound is selected such that it remains water-soluble and base-soluble and does not flocculate in said stream;
wherein said stream is contacted with said compound either before or at the same time as said stream enters said basic wash unit operation.
The second aspect of the instant claimed invention is a method to inhibit the polymerization of a carbonyl compound in a basic wash unit operation in a hydrocarbon cracking process, comprising:
adding a compound selected from the group consisting of
alpha-amino acids and esters thereof and amides thereof and salts thereof and mixtures thereof to a basic wash unit operation; and
providing a stream comprising a carbonyl compound to said basic wash unit operation;
wherein said compound is selected such that it remains water-soluble and base-soluble and does not flocculate in said stream or said basic wash unit operation; and
wherein said compound is added to said basic wash unit operation before or while said stream enters said basic wash unit operation.
The third aspect of the instant claimed invention is a method to inhibit the polymerization of a carbonyl compound in a basic wash unit operation in a hydrocarbon cracking process, comprising:
contacting a stream comprising at least one carbonyl compound with a compound selected from the group consisting of
Mercaptoacetic acid and alkyl esters thereof and salts thereof and mixtures thereof,
wherein said compound is selected such that it remains water-soluble and base-soluble and does not flocculate in said stream;
wherein said stream is contacted with said compound either before or at the same time as said stream enters said basic wash unit operation.
The fourth aspect of the instant claimed invention is a method to inhibit the polymerization of carbonyl compounds in a basic wash unit operation in a hydrocarbon cracking process, comprising:
adding a compound selected from the group consisting of
Mercaptoacetic acid and alkyl esters thereof and salts thereof and mixtures thereof to a basic wash unit operation; and
providing a stream comprising a carbonyl compound to said basic wash unit operation;
wherein said compound is selected such that it remains water-soluble and base-soluble and does not flocculate in said stream or said basic wash unit operation; and
wherein said compound is added to said basic wash unit operation before or while said stream enters said basic wash unit operation.
For purposes of this patent application, the following terms have the indicated meanings:
xe2x80x9cacetaldehydexe2x80x9d is CH3CHO, and has a CAS Registry Number of 75-07-0. It is also known as acetic aldehyde, aldehyde, ethanal or ethyl aldehyde.
xe2x80x9cphenylacetaldehydexe2x80x9d is C6H5CH2CHO, and has a CAS Registry Number of 122-78-1. It is also known as xcex1-toluic aldehyde.
xe2x80x9cAldrichxe2x80x9d refers to Aldrich Chemical Company, P.O. Box 2060, Milwaukee, Wis., 53201 U.S.A. telephone number (800) 558-9160, fax number (800) 962-9591.
xe2x80x9calkylxe2x80x9d refers to a fully saturated hydrocarbon radical of from one to 10 carbon atoms.
xe2x80x9camino acidxe2x80x9d is an organic acid containing both a basic amino group {xe2x80x94NH2} and an acidic carboxyl group {xe2x80x94COOH}.
xe2x80x9cxcex1-amino acidxe2x80x9d refers to organic acid containing both a basic amino group {xe2x80x94NH2}and an acidic carboxyl group {xe2x80x94COOH}, where the amino group {xe2x80x94NH2} is attached to the carbon atom next to the acidic carboxyl group{xe2x80x94COOH}. Throughout the remainder of this patent application xe2x80x9cxcex1-amino acidxe2x80x9d will be written as xe2x80x9calpha-amino acidxe2x80x9d.
xe2x80x9carylxe2x80x9d refers to a single aromatic ring radical of 6 carbon atoms or to two or three fused aromatic rings (radical) of from 10 to 13 carbon atoms.
xe2x80x9cBachemxe2x80x9d refers to Bachem California, Inc., USA, 3132 Kashiwa Street, Torrance, Calif. 90505, telephone number (310) 539-4171.
xe2x80x9cbenzylxe2x80x9d refers to the xe2x80x94CH2xe2x80x94C6H5 radical.
xe2x80x9cLancasterxe2x80x9d refers to Lancaster Synthesis, Inc., P.O. Box 1000, Windham, N.H. 03087-9977, U.S.A., telephone number (800) 238-2324, fax number (603) 889-3326.
xe2x80x9cMercaptoacetic acidxe2x80x9d is also known as xe2x80x98thioglycolic acidxe2x80x99, CAS Registry No. 68- 11- 1. The molecular formula for Mercaptoacetic acid is HSCH2COOH. Mercaptoacetic acid can also be described as a moiety where the nitrogen of Glycine has been replaced by a sulfur atom.
xe2x80x9cmmolesxe2x80x9d refers to millimoles.
xe2x80x9cradicalxe2x80x9d refers to a moiety that has one bond available for attachment to another moiety.
The carbonyl compounds that are known to polymerize in a basic wash unit operation present in a hydrocarbon cracking process, include, but are not limited to, aldehydes and ketones. Specific polymerizable moieties within these general categories include, but are not limited to, acetaldehyde and phenylacetaldehyde.
The first aspect of the instant claimed invention is a method to inhibit the polymerization of a carbonyl compound in a basic wash unit operation in a hydrocarbon cracking process, comprising:
contacting a stream comprising at least one carbonyl compound with a compound selected from the group consisting of
alpha-amino acids and esters thereof and amides thereof and salts thereof and mixtures thereof;
wherein said compound is selected such that it remains water-soluble and base-soluble and does not flocculate in said stream;
wherein said stream is contacted with said compound either before or at the same time as said stream enters said basic wash unit operation.
Basic wash unit operations in which this method can be used, include, but are not limited to, caustic scrubbers, caustic towers, amine acid gas scrubbers, benzene strippers and spent caustic oxidizers.
Alpha-amino acids are known to people of ordinary skill in the art of organic chemistry. They are available commercially or capable of being synthesized by people of ordinary skill in the art of organic chemistry.
Preferable alpha-amino acids suitable for use in the method of the instant claimed invention are selected from the group consisting of:
Alanine (also known as xcex1-alanine; xcex1-aminopropionic acid; and 2-aminopropanoic acid),
Asparagine (also known as xcex1-aminosuccinamic acid; (xcex2-asparagine; althein; aspartamic acid; and aspartamide),
Aspartic acid (also known as asparaginin acid; asparagic acid; and aminosuccinic acid),
Cysteine (also known as xcex1-amino-xcex2-thiolpropinonic acid; and xcex2-mercaptoalanine),
Homocysteine (also known as 2-amino-4-mercaptobutyric acid),
Glutamine (also known as 2-amino-4-carbamoylbutanoic acid),
Glutamic Acid (also known as xcex1-aminoglutaric acid; and 2-aminopentanedioic acid),
Glycine (also known as aminoacetic acid),
Histidine (also known as xcex1-amino-xcex2-imidazolepropionic acid),
Isoleucine (also known as 2-amino-3-methylpentanoic acid; and Ile),
Leucine (also known as xcex1-amino-xcex3-methylvaleric acid; and xcex1-aminoisocaproic acid),
Methionine (also known as 2-amino-4-(methylthio)butyric acid),
Phenylalanine (also known as xcex1-amino-xcex2-phenylpropionic acid),
Serine (also known as xcex2-hydroxyalanine; and xcex1-xcex1-xcex2-hydroxypropionic acid),
Threonine (also known as xcex1-amino-xcex2-hydroxybutyric acid),
Tryptophan (also known as indole-xcex1-aminopropionic acid; and 1-xcex1-amino-3-indolepropionic acid),
Tyrosine (also known as xcex2-p-hydroxyphenylalanine; and xcex1-amino-xcex2-p-hydroxyphenylpropionic acid) and
Valine (also known as xcex1-aminoisovaleric acid);
and esters thereof and amides thereof and salts thereof and mixtures thereof.
Preferred alkyl esters of alpha-amino acids include, but are not limited to, the ethyl ester of Cysteine and the ethyl ester of Alanine.
Aryl esters of alpha-amino acids are known in the art of alpha-amino acids.
Preferred benzyl esters of alpha-amino acids include, but are not limited to,
Glycine benzyl ester hydrochloride (CAS Registry No. 1738-68-7),
Alanine benzyl ester hydrochloride (CAS Registry No. 5557-83-5), and
Serine benzyl ester hydrochloride (CAS Registry No. 1738-72-3).
Preferred amides of alpha-amino acids include, but are not limited to Glycinamide hydrochloride (CAS Registry Number 1668-10-6).
These alpha-amino acids and derivatives thereof are available commercially through Aldrich or Lancaster or Bachem or can by synthesized by persons of ordinary skill in the art of organic chemistry.
The more preferred alpha-amino acids suitable for use in the method of the instant claimed invention are selected from the group consisting of Glycine, Histidine, Alanine, Cysteine, the ethyl ester of Cysteine, the ethyl ester of Alanine and mixtures thereof and salts thereof.
The most preferred alpha-amino acids are Glycine and Cysteine and mixtures thereof and salts thereof.
Glycine is one of the most preferred alpha-amino acids because it has been found that when a Glycine-acetaldehyde oligomer or Glycine-aldol oligomer is formed, these materials act as dispersants for themselves and for any other foulants known to be present.
The amount of compound added to said stream comprising a carbonyl compound or to the basic wash unit operation is from about 0.01 ppm to about 10,000 ppm, preferably from about 0.1 ppm to about 1000 ppm, and most preferably from about 1 ppm to about 100 ppm.
The particular compound selected must be capable of remaining water-soluble and base-soluble throughout the stream and the basic wash unit operation. If the compound loses solubility and begins to flocculate another compound should be selected. Flocculation of the compound is undesirable because it prevents the alpha-amino acid from inhibiting the polymerization of carbonyl compounds.
Typically, the compound is formulated to be a mixture of an alpha-amino acid, a base and water. One such typical formulation is 25% Glycine, 20% NaOH (50% aq. sol""n) and 55% deionized water. The purpose of adding base to the formulation is to inhibit the growth of microorganisms in the alpha-amino acids.
The compound may be added to the stream comprising a carbonyl compound before the streams"" entry into the basic wash unit operation. The compound may be added to the stream comprising a carbonyl compound at the same time the stream enters the basic wash unit operation.
In addition to the previously described methods of adding the compound to the stream, the compound may be added to the basic wash unit operation before or while the stream comprising a carbonyl compound enters the basic wash unit operation. The compound may be added to the basic wash unit operation by adding it to whatever base is being used in the basic wash unit operation.
It is preferred to add the compound directly to the basic wash unit operation, before the entry of the stream comprising a carbonyl compound.
These alpha-amino acids have been found to react with any carbonyl compounds present in said stream to yield stable, water-soluble derivatives that do not form polymer on exposure to base. Thus by adding alpha-amino acids to streams comprising carbonyl compounds or to basic wash unit operations in a hydrocarbon cracking process, the undesirable polymerization of the carbonyl compounds can be inhibited.
This invention has the added benefit that the alpha-amino acids suitable for use are considered a xe2x80x9cgreenxe2x80x9d chemistry that makes them highly desirable for field applications.
It has also been found possible to inhibit the undesirable polymerization of carbonyl compounds by adding a compound selected from the group consisting of Mercaptoacetic acid, alkyl esters thereof, salts thereof and mixtures thereof to either the stream comprising the carbonyl compound or to the basic wash unit operation itself. Mercaptoacetic acid and its alkyl esters and salts are available commercially, through Aldrich and other companies, or can be synthesized using techniques known in the art of organic chemistry.